Mineral-coated, galvanized steel article



Feb. 6, 1968 E. T. SCHWENDEMANN 3,367,753

MINERAL-COATED, GALVANIZED STEEL ARTICLE Filed June 22, 1965 UnitedStates Patent Ofiice 3,367,753 Patented Feb. 6, 1968 3,367,753MINERAL-COATED, GALVANIZED STEEL ARTICLE Edward T. Schwendemann,Highland, Ind., assignor to Inland Steel Company, Chicago, Ill., acorporation of Delaware Filed June 22, 1965, Ser. No. 465,863 7 Claims.(Cl. 29195) The present invention relates generally to steel-basegalvanized articles produced by a hot-dip process. More particularly theinvention relates to a steel-base galvanized article which isspangle-free on at least one surface, which is substantially devoid ofiron-zinic intermetallic compounds at the interface between the zinccoating and the steel base of the article, and which is readilypaintable with a top coating of oil-base, stearate-containing paintwithout forming flake-causing zinc stearates between the zinc layer andthe stearate-containing coating of paint.

Conventional galvanized steel articles, such as galvanized steel stripor sheet having a pair of opposed surfaces, usually exhibit a spangledor frosty surface appearance. It is oftentimes desired to paint at leastone of the two opposed surfaces of a galvanized steel article; and, inorder to obtain a more adherent coating of paint, it is desirable thatthe galvanized steel article be free of spangles on the surface to bepainted.

Certain conventional methods heretofore used for eliminating spanglehave drawbacks in that such methods have required subjecting thegalvanized steel article to a heat treatment which also causes theformation of ironzinc intermetallic compounds at the interface betweenthe steel base and the zinc coating and in the zinc coating itself.These iron-zinc intermetallic compounds are relatively brittle comparedto the steel base or zinc coating, and are thus undesirable.

Moreover, a heat treatment eliminates spangles on both surfaces of thegalvanized article undergoing heat treatment so that it is not possibleto thus produce an article which would be spangle-free on one side andspangled on the other; and this type of article is oftentimes desired.

When the zinc coating on a conventional galvanized steel article iscovered with a layer of paint having a stearate base, the stearates inthe paint react with the zinc, forming zinc stearates which are soapsand which produce a plane of weakness between the zinc coating and thepaint layer; and this causes the paint to flake off the galvanized steelarticle. A paint having a stearate base consists essentially of thestearate base plus pigment.

All of the above-mentioned drawbacks, arising with conventionalgalvanized steel articles, are eliminated in accordance with the presentinvention by subjecting the galvanized steel article to a treatment,immediately after the steel base is coated with molten zinc and beforethe zinc has solidified, in which treatment a layer of finely divided,particulate mineral material is unifor'inly distributed across the topof the zinc coating to cover the coating. The particulate mineralmaterial forms an adherent layer on the zinc coating and prevents theformation of spangles on the surface of the zinc coating. Each of theindividual particles of finely divided mineral mate rial would be anucleus for spangle formation, but the individual particles are appliedso closely together that none of the nuclei has a chance to grow,thereby eliminating the appearance of spangles. The resulting appearanceis a smooth, spangle-free, usually gray surface on the zinc coating.

The layer of fine, particulate mineral material may be applied to one orboth of the two opposed surfaces of the galvanized steel article; and,in the former case, the galvanized article would have spangles on oneside but not on the other. In either case, both surfaces are alsosubstantially devoid of iron-zinc intermetallic compounds, a situationnot obtained when spangles are eliminated by subjecting the galvanizedarticle to a heat treatment.

Galvanized strip is generally produced on a continuous line; and, whenthis line contains a heat treating portion for elimination of spangles,the operation of the line is oftentimes slowed. The slow-down is causedby moving the strip through the heat treating furnace relatively slowlyso as to subject the strip to the amount of heating required to avoidspangles. The alternative to a slow-down is a relatively long furnace,but this increases equipment costs substantially.

Because no heat treatment is required with the method of the presentinvention, there is neither a slow-down nor a need to provide costlyfurnaces in the galvanizing line in order to avoid spangles. I

The surface of the galvanized article, being free of spangles, isreadily paintable with all kinds of paint. If the paint has a stearatebase, the stearates in the paint cannot react with the zinc in thegalvanized coating because the layer of fine, particulate mineralmaterial covering the zinc coating acts as a barrier and prevents theformation of zinc stearates. This minimizes fiaking of paint from thepainted article.

The present invention also eliminates the necessity of subjecting thegalvanized article to a bonderizing treatment preparatory to painting.Bonderizing is a treatment in which a galvanized surface is prepared forpainting by treating the surface with a phosphate solution to form asmooth, thin film, composed largely of zinc phosphate, on the surface ofthe galvanized article.

Other features and advantages are inherent in the article and methodclaimed and disclosed, or will become apparent to those skilled in theart from the following detailed description in conjunction with theaccompanying diagrammatic drawings wherein:

FIGURE 1 i a diagram illustrating an embodiment of a method, inaccordance with the present invention, for producing a paint-adherent,galvanized article in accordance with the present invention; and

FIGURE 2 is a sectional view of an embodiment of an article inaccordance with the present invention.

Referring initially to FIGURE 1, a steel strip 10 moves downwardlythrough a chute 11 extending below the sun face 15 of a molten bath 13of metal consisting essentially of zinc. Bath 13 is contained within avat 12. Steel strip 10 passes under a roller 14, near the bottom of vat12, moves upwardly above the surface 15 of bath 13, passes over a roller16, and then moves in a horizontal direction to a coiling or shearingstation (not shown) or to such other operations or treatments as may bedesired.

As the steel strip 10 passes through molten bath 13, both surfaces ofthe steel strip are coated with zinc. The zinc coating generallysolidifies below roller 16, in a space having lower and upper limitsdelineated by the two dashdot lines 17, 18. Everything described up tothis point, with reference to FIGURE 1, is conventional.

In accordance with the present invention, before the zinc coatingsolidifies, it is covered with a layer of finely divided, particulatemineral material. In a typical embodiment, the mineral material isapplied to the zinc coating by nozzles 19, 20, each located on arespective opposite side of the galvanized strip 10, below thesolidification zone 1748.

Each nozzle 19, 20 is connected by a respective line 21, 22, having arespective shut-off valve 23, 24, to a common line 25 communicating withblower means 26 for providing an air blast through lines 25, 21 and 22.The finely divided, particulate mineral material 32 is stored in ahopper 28 and enters line 25 through a feed conduit 27 extending betweenhopper 28 and line 25.

When valve 23 is open, the mineral material is applied to thezinc'surface coating 31 most closely adjacent nozzle 19; and when valve23 is closed, surface 31 is free of finely divided, particulate mineralmaterial. The same is true for the zinc surface coating 30 passing mostclosely adjacent nozzle 20. The application of finely divided,particulate mineral material to coating 30 depends upon whether valve 24is open or closed.

The article 29 illustrated in FIGURE 2 is produced when valve 23 isclosed, and valve 24 isopen. Article 29 includes a steel base 10 havinga pair of opposite sides 40, 41; and each side is covered by a metalliccoating 30, 31, respectively, with said coating consisting essentiallyof zinc.

Uniformly distributed on and covering zinc coating 30 is an adherentlayer of finely divided, particulate mineral material 32.

The interfaces between steel base 10 and metallic coatings 30, 31 aresubstantially devoid of iron-zinc intermetallic compounds, as arecoatings 30, 31; and metallic coating 30 is devoid of observablespangles.

Because zinc coating 30 is not fully solidified at the time theparticles of mineral material 32 are applied thereto by nozzles 19, 20,coating 30 is in a tacky condition to which the particles of mineralmaterial readily adhere, thereby preventing the particles from droppinginto molten zinc bath 13 during application of the mineral material. Thebond resulting from application of the particles under the conditionsdescribed in the preceding sentence is hereinafter called athermomechanical bond.

Steel base 10 may have any of the compositions conventionally used forthe steel base of galvanized articles. Molten bath 13 consistsessentially of zinc and may also contain traces of aluminum and/or otherelements conventionally added to baths of molten galvanizing material.

Among the compositions of mineral material which may be utilized inaccordance with the present invention, conventional Portland cement hasbeen found to be very satisfactory. Hackhs Chemical Dictionary, Thirdedition, McGraw-Hill Book Company, Inc., New York, 1944, definesPortland cement as a fine, gray powder, probably containing 3CaO.SiO3CaO.Al O and 2CaO.SiO and having a particle size of 200 mesh.

Other examples of compositions which may be used as the mineral materialare dolomite (CaCO .MgCo alumina (A1 kyanite (A1 O .SiO mullite (2SiO.3A1 O iron oxide dust from conventional blast furnace or basic oxygenconverter operations, silica (SiO and lime (CaO).

The fine particles of mineral material should be uniformly distributedon the zinc coating in a quantity sulficient to prevent formation ofobservable spangles. The amount of mineral material to be applied may bedetermined visually. If visible spangle growth occurs, this is anindication that insufficient mineral material has been applied.Generally, it is sufficient to apply the mineral material in an amountwhich completely covers the zinc coating. Typically, Portland cement inan amount between 0.352 and 0.00352 ounce per square foot of galvanizedsurface may be applied. The amount of mineral material to be applied isindependent of the thickness of the zinc coating and independent of thethickness of the steel base.

From the standpoint of particle size, 200 mesh has been found to besatisfactory; and the particle size should, preferably, not exceed mesh.

The foregoing detailed description has been given for clearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom, as modifications will be obvious to those skilled in the art.

What is claimed is:

1. A galvanized steel article capable of being coated with astearate-base paint, said article comprising:

a steel base having a pair of opposed sides;

a metallic coating, consisting essentially of zinc, covering at leastone of said sides;

and an adherent layer of finely divided, particulate mineral materialwherein each particle is embedded and thermo-mechanically bonded on saidmetallic coating and completely covering said coating to provide abarrier against the formation of zinc-stearate compounds on the metalliccoating.

2. A galvanized steel article as recited in claim 1 wherein: i

said finely divided, particulate mineral material is Portland cement;and

said layer of finely divided, particulate mineral material is evenlydistributed on said metallic coating in an amount between 0.00352 and0.352 ounce per square foot of metallic coating.

3. A galvanized steel article as recited in claim 1 wherein said mineralmaterial has a particle size no greater than 170 mesh. 1

4. A galvanized steel article as recited in claim 1 wherein saidthermo-mechanically bonded particles are spaced so closely together thatthe metallic coating is devoid of observable spangles.

5. A galvanized steel article as recited in claim 4 and comprising aspangled, metallic coating, consisting essentially of zinc, on the otherside of said steel base.

6. A galvanized steel article as recited in claim 1 and comprising:

a coating of paint covering said layer of mineral material; said paintconsisting essentially of a stearate base plus pigment;

said article being substantially devoid of zinc-stearate compoundsbetween the metallic coating and the coating of paint.

' 7. A galvanized steel article as recited in claim 1 wherein saidmineral material is selected from the group consisting essentially ofPortland cement, dolomite, alumina, kyanite, mullite, iron oxide dust,silica and lime.

References Cited UNITED STATESPATENTS 1,268,987 6/1918 McMullen 29196.5X 1,984,335 12/1934 Crapo 29-1965 X 2,121,574 6/1938 Romig 29196.5 X2,231,967 2/1941 Tainton 29-l96.5 X 2,724,177 11/1955 Colfman 29196.5 X2,994,126 8/1965 Kennedy 29-19615 X 3,056,694 10/1962 Mehler 29-1965 'X3,155,530 11/1964 Schnedlev 29l95 HYLAND BIZOT, Primary Examiner.

1. A GALVANIZED STEEL ARTICLE CAPABLE OF BEING COATED WITH ASEARATE-BASE PAINT, SAID ARTICLE COMPRISING: A STEEL BASE HAVING A PAIROF OPPOSED SIDES; A METALLIC COATING, CONSISTING ESSENTIALLY OF ZINC,COVERING AT LEAST ONE OF SAID SIDES; AND AN ADHERENT LAYER OF FINELYDIVIDED, PARTICULATE MINERAL MATERIAL WHEREIN EACH PARTICLE IS EMBEDDEDAND THERMO-MECHANICALLY BONDED ON SAID METALLIC COATING AND COMPLETELYCOVERING SAID COATING TO PROVIDE A BARRIER AGAINST THE FORMATION OFZINC-STEARATE COMPOUNDS ON THE METALLIC COATING.